Piezoelectric actuators have many applications. In particular, piezoelectric diaphragms have been employed as pressure sensors, in speakers for audio equipment, and fluid ejection, fluid pumping, and printing applications. One specific application for piezoelectric actuators is as jetting drivers in ink jet print heads.
FIGS. 1A and 1B illustrate one example of a single ink jet 10 that is suitable for use in an ink jet array print head. The ink jet 10 has a body that defines an ink manifold 12 through which ink is delivered to the ink jet print head. The body also defines an ink drop-forming orifice, or nozzle, 14 together with an ink flow path from ink manifold 12 to nozzle 14. In general, the ink jet print head preferably includes an array of closely spaced nozzles 14 for use in ejecting drops of ink onto an image-receiving medium (not shown), such as a sheet of paper or a transfer drum. Ink jet print heads can have a plurality of manifolds for receiving various colors of ink.
Ink flows from manifold 12 through an inlet port 16, an inlet channel 18, a pressure chamber port 20, and into an ink pressure chamber 22. Ink leaves pressure chamber 22 by way of an outlet port 24 and flows through an outlet channel 28 to nozzle 14, from which ink drops are ejected.
Ink pressure chamber 22 is bounded on one side by a flexible diaphragm 30. A piezoelectric transducer 32 is secured to diaphragm 30 by any suitable technique and overlays ink pressure chamber 22. Metal film layers 34, to which an electronic transducer driver 36 can be electrically connected, can be positioned on either side of piezoelectric transducer 32.
Piezoelectric transducer 32 is operated in its bending mode such that when a voltage is applied across metal film layers 34, transducer 32 attempts to change its dimensions. However, because it is secured rigidly to the diaphragm 30, piezoelectric transducer 32 bends, deforming diaphragm 30, thereby displacing ink in ink pressure chamber 22, causing the outward flow of ink through outlet port 24 and outlet channel 28 to nozzle 14. Refill of ink pressure chamber 22 following the ejection of an ink drop is augmented by reverse bending of piezoelectric transducer 32 and the concomitant movement of diaphragm 30, which draws ink from manifold 12 into pressure chamber 22.
To facilitate manufacture of an ink jet array print head, ink jet 10 can be formed of multiple laminated plates or sheets. These sheets are stacked in a superimposed relationship. Referring once again to FIGS. 1A and 1B, these sheets or plates include a diaphragm plate 40, which forms diaphragm 30 and a portion of manifold 12; an ink pressure chamber plate 42, which defines ink pressure chamber 22 and a portion of manifold 12; an inlet channel plate 46, which defines inlet channel 18 and outlet port 24; an outlet plate 54, which defines outlet channel 28; and an orifice plate 56, which defines-nozzle 14 of ink jet 10. The piezoelectric-transducer 32 is bonded to diaphragm 30, which is a region of diaphragm plate 40 covering ink pressure chamber 22.
The jet driver design plays a major role in determining the performance characteristics of the inkjet printhead. For example, jet efficiency depends upon, among other things, the dimensions of the piezoelectric transducer in relation to the diaphragm. In order to achieve jetting device packing densities required by high resolution printing, more efficient actuator designs that can increase the volumetric displacement of the ink chamber for a given driver voltage are desired.
Also, performance variation of inkjet devices caused by piezoelectric transducer alignment error within a monolithic printhead is a recognized problem in the manufacture of inkjet printheads. For example, the required jetting voltage of individual inkjets can vary to an unacceptable degree with the misalignment of the piezoelectric transducer relative to the diaphragm. This sensitivity of the jetting voltage to misalignment of the piezoelectric transducer is undesirable, and requires tight manufacturing tolerances. Therefore, improved inkjet printhead designs with reduced sensitivity are desired.